feat(docs): use spl-core's documentation settings and drop the workarounds

[ubmarco]

Stacked on #2. This branch pins spl-core to a commit of the useblocks fork that adds the settings #2 was missing, and deletes the workarounds #2 needed without them. It also brings in the two upstream commits the fork lacked, so the branch is 0 commits behind avengineers/SPLed develop.

spl-core changes: useblocks/spl-core#4, five commits on top of spl-core 8.9.0.

What changes

spl-core setting	What SPLed gains or deletes
SPL_SOURCE_DOCS_JINJA_RAW_TAGS OFF	Generated listings carry no {% raw %} markers. conf.py's source-read strip is gone, and conf.py registers no handler at all.
SPL_VARIANT_DATA_FILE_DOCS / _REPORTS	spl-core passes each build its cell as -D needs_variant_data_file=. The fixed-name build/variant-data-*.json copies and conf.py's variant selection are gone. Tests and the VS Code task select a cell the same way, with the key ubc check -c overrides.
SPL_SPHINX_BINARY_DIR = generated	The report pages have stable names, generated/components/<c>/reports/..., so the report sections name them directly and no document globs /build/**. Coverage links follow the pages. conf.py prunes build from the walk and forwards only spl-core's generated/ patterns, and the generated/** rule keeps them out of docs builds.
KConfig.declared_boolean_symbols()	The kconfiglib fallback in tools/variant_data.py is gone.

On Windows without Developer Mode, generated now becomes a junction rather than a marker directory, because the report pages are read through it.

The upstream merge

The first commit merges avengineers/SPLed develop: spl-core 8.9 with a refreshed lock, and the light controller state machine fix. The commit message lists how each conflict was resolved.

One conflict only showed at run time. The refreshed lock brings sphinx-needs 8.5.0, which resolves the variant data right after loading needs_from_toml. #2's conf.py selected the file later, at config-inited priority 20. With 8.5.0 every build therefore either failed on a missing build/autoconf.json or quietly read that pointer instead of its cell, which leaves a reports build without reports. The merge fixes that at priority 10. The last commit replaces the mechanism with the command-line override, which sphinx-needs keeps ahead of the TOML.

Verification

• Documentation tests, test_documentation.py, test_ubproject_config.py and test_variant_data.py: 94 passed, 1 skipped (the ubc requirement check, which only runs in CI).
• CI documentation gate, pytest -m "docs and gate_develop_pr" with CI_REQUIRE_UBC=1 and ubc 0.35.0: 31 passed, on this branch and on the merge and accessor commits below it.
• End to end on Linux, gcc 16, CMake 4.4: Disco test kit reports and docs targets. Every report page sits under generated/, both kinds of coverage link resolve, the verification sections render in the reports build and not in the docs build, and SplBuild finds all 16 report artifacts. A docs build whose generated link was re-pointed at another directory stops with spl-core's message.
• Full CI, started manually on this branch: green on Windows, Linux, the devcontainer and the documentation gate. On Windows, 92 passed and 12 skipped, including every variant's reports test through generated. https://github.com/useblocks/SPLed/actions/runs/35985268428
• The Windows log does not show whether the runner got a symlink or the junction fallback. The fallback itself is covered by test_a_refused_symlink_falls_back_to_a_junction.

Unchanged here

• spl-core's per-component wrapper pages generated/reports/*_index.md are not in any toctree. That gives five warnings on Disco, as before under build/.
• The integration suite's source listings define the same implementation needs as the components' own listings, which gives five duplicate-ID warnings on Disco, as before.